The present method of HUD tray harmonization illustrated in FIG. 1, consists of several cumbersome and tedious steps which comprise levelling of the entire aircraft 2, e.g., by utilizing hydraulic jacks and special level readers, the positioning of a target board 4 at a substantial distance L from the aircraft, e.g., at a distance of at least 25 m, the alignment of the target board with respect to height and angular orientation relative to the aircraft, mounting a telescope on a Mount Alignment Jig (MAJ), and adjusting the tray's disposition until the cross marks of the telescope and target coincide, and then tightly closing the connecting screws of the tray to lock the tray in the aligned position. It can be easily realized that such a procedure, which must be carried out outside a hangar, requires hard labor involved in levelling huge aircrafts and also suffers from the drawbacks of having to install and align a target at an open field, which target may be affected by prevailing winds and rain, and the costly personnel and equipment required, not to speak of the time necessary for performing such tasks.